In modern cellular radio systems, the radio network has a strict control on the behaviour of the terminals in the network. Uplink transmission parameters, i.e. parameters for the transmission over a communication channel from a terminal (also called UE in WCDMA terminology) to a base station (also called node B in WCDMA terminology), to be controlled are for example frequency, timing, and power. The uplink transmission parameters are regulated via downlink control signalling from the base station to the terminal.
In order to enable control of the terminal, measurements on uplink signals are required. Determination of timing misalignment requires that the base station perform a comparison of the timing of the received signal with a reference clock signal from a reference clock in the base station. Timing misalignment is caused by unforeseen propagation delay and mutual drift between the reference clock in the base station and a clock in the terminal. Likewise, the determination of the transmit power requires determination of the signal power of the signals received in the base station in relation to a predetermined threshold. The received power is not only depending on transmit power of the terminal but also on signal attenuation during propagation. The latter will vary with time.
Uplink radio communication over the communication channel between the terminal and the base station is subjected to multi path propagation, fading, frequency errors, round trip propagation times etc. This uplink communication channel is often referred to as an air interface. It is common that bit errors and block errors arise in information transmitted via said air interface. An uplink receiver of a base station is arranged so as to reduce bit error and block error rates. One essential part of a base station receiver is a channel estimation unit arranged to estimate the uplink communication channel.
Whenever a DFT (implemented as an FFT) is used by the base station receiver on a time domain signal, said time domain signal is assumed to be periodic with period time equal to the length of the DFT. In order to ensure this for signals subject to dispersive channels, a cyclic prefix can be used. The cyclic prefix must have a length that is larger, or equal to, the delay spread of the uplink communication channel. Also, any timing misalignments should have lower resolution than the cyclic prefix. Thus, an algorithm for determination of timing misalignment has preferably a resolution which is lower than the length of this cyclic prefix.